The present invention relates to ignition systems for internal combustion engines in general and more particularly to an ignition plug for igniting the air/fuel mixture within the combustion chamber.
Ignition plugs, or spark plugs, are used in most internal combustion engines to provide relatively high voltage energy which is used to ignite the air/fuel mixture within the combustion chamber of the engine. The ignition plugs are mounted into the cylinder head and extend into the combustion chamber of the internal combustion engine. There is a terminal on the portion of the ignition plug external to the engine which is attached by a wire to the ignition system on one side and to a center electrode on the other. The portion of the ignition plug which is internal to the engine holds a ground electrode and the center electrode which are exposed to the combustion chamber. The electrodes are situated such that they face each other with a gap in between.
In general, when an engine is running, relatively high voltage energy is delivered to the ignition plug at the correct moment by the ignition system. When the voltage is applied across the gap, a charge builds on the center electrode causing electrons to cross the gap between the ground electrode and the charged center electrode, thereby producing sparks. In common negative ground ignition systems, the electron flow across the gap is from the ground (negative) electrode to the center (positive) electrode. The sparks ignite the air/fuel mixture which is contained within the combustion chamber, thereby providing the engine with power. The combustion process starts by the energy of the electron flow across the gap between the electrodes igniting the fuel-air mixture that passes the ignition plug when it is firing. Energy is released from the resulting chemical reaction between the fuel and oxygen. This energy is in the form of high temperature combustion product molecules moving at a high speed. These molecules collide with adjacent air/fuel mixture and transferring sufficient heat energy to ignite the mixture. In this way the combustion quickly spreads through the combustion chamber. The spread of combustion is aided by the high velocities that the air/fuel mixture experiences as a result of being introduced into the combustion chamber and being compressed by the piston.
Typically, however, a substantial portion of the fuel within the combustion chamber is not burned. This is a result of a variety of factors including shielding, limited ignition presentation and poor aerodynamic flow of the air/fuel mixture within the combustion chamber.
Shielding occurs when the ground electrode itself or some other structure blocks some of the air/fuel mixture from being in the direct path of the propagation of combustion initiated by the ignition. Shielding is a common disadvantage in ignition plugs having a ground electrode that is bent over the end of the center electrode thereby blocking the air/fuel mixture contained behind the ground electrode from igniting.
A related disadvantage common in such ignition plugs is that there is a limited region of ignition presentation available for ignition of the air/fuel mixture. This is because there is a small gap area which limits the ignition to a very small region near the plug tip. This limited ignition region limits the opportunity that the fuel has of coming into contact with the ignition and thereby limits the amount of fuel that can be ignited.
Another disadvantage of conventional ignition plugs is that they are not aerodynamically designed. Air/fuel mixture and burning fuel circulates about the combustion chamber at high velocities during ignition. The combustion chamber itself has a cylindrically shaped, smooth interior surface which allows for the aerodynamic movement of air/fuel mixture. Known ignition plugs, however, contain abrupt or sharp surfaces, edges and discontinuities in the tip area which have poor aerodynamics and impede the movement of air/fuel mixture. This is particularly a problem considering that the ignition is located within the tip area, and the air/fuel should flow most freely there to guarantee that most of it is ignited.
Due to the shielding, limited ignition presentation and non-aerodynamic design, only some of the fuel is ignited. This makes the power output of the engine less than it would be if all of the fuel were burned. Moreover, the engine is less efficient and, therefore, does not get the fuel economy it would otherwise get. A further result of the inefficient burn is that the fuel which is not burned is forced out of the combustion chamber along with the exhaust gasses. Unburned fuel is a worse pollutant than burned fuel and, therefore, an engine which does not burn all of the fuel during ignition creates more pollution than an efficient engine which does.
Another disadvantage occurring with conventional ignition plugs is in setting the gap. Typically, the gap is set by manually bending the ground electrode to obtain the proper gap. The bending process is often imprecise and/or often becomes inadvertently misaligned after prolonged engine operation.
In U.S. Pat. No. 1,325,439, a spark plug is described that has a ring-shaped ground electrode. This construction improves the presentation of spark by allowing spark generation in a circle between the ground and center electrodes. Moreover, this configuration creates less shielding than a conventional plug in the axial direction. However the semicircular crossectional shape of the ground electrode presents a flat surface towards the center electrode and has significant surface discontinuities at the juncture of the flat inner surface and the rounded outer surface. This structure results in poorer aerodynamics of the air/fuel mixture and particularly of the combustion products propagating away from the gap.
In U.S. Pat. No. 1,495,499, a spark plug is described that has a coil-shaped ground electrode and a star-shaped center electrode providing four gaps to generate sparks in four discrete locations. The ground electrode is round in crossection, but has discontinuities at its free end. This and the structure of the arms of the center electrode decrease the aerodynamics of the plug tip.
U.S. Pat. No. 1,666,853 describes a spark plug having a ring-shaped ground electrode. The circular electrode is positioned at an angle to the center electrode which results in a varying gap dimension and decreased spark presentation.
Accordingly there is a need in the art for an ignition plug that will provide improved aerodynamics, spark presentation and less shielding.